The present invention relates generally to heating coil assemblies and, more particularly, to a support for heating coil assemblies and methods for assembling the same.
Electric heating elements using helical wire heating coils are well known in the art. A helical wire heating coil is typically mounted on a supporting structure and strung between a number of ceramic insulating elements which provide direct support for the coil and isolate the coil from the supporting structure which is generally some type of metal framework. If is important that the insulating element hold the coil against both lateral displacements out of the supporting member and movement in the direction of the axis of the coil. Thus, it is common in prior art ceramic insulating supports to capture one or more turns of the helical coil to hold the same against lateral displacements and axial movement.
A prior art heating coil assembly with insulating supports is shown in U.S. Pat. No. 5,122,640. There, the insulating support has notches that include lead-in ramp surfaces to spread two halves of the coil turn until the coil is centrally positioned in the notch. A portion of the coil turns rest on the faces of the support body to preclude axial movement of the coil once it is locked into position. The notch has four separate abutments to further prevent dislodgment. A problem with this construction is that a fair portion of the coil turn contacts the surface of the insulating support. Over time, after the coil is energized, hot spots will form at the locations where the coil makes contact with the insulating support. This may lead to uneven heating and reduces the life of the heating coil. Moreover, the support notches shown in U.S. Pat. No. 5,122,640 have an outer abutment means that project inwardly of the outer edge portion of the notch for engaging the outer surface of the coil turn. This forces the coil to be within the outer edges of the insulating support. This type of design along with the assembly layout inhibits good air circulation. The patent also shows that the assembly is held together by two separate rails.
A heating coil assembly is also shown in U.S. Pat. Nos. 248,943 and 4,250,399, which are owned by the assignee of the present invention and incorporated herein by reference in their entirety. The notches or slots shown in those patents require less contact between the heating coil and the insulating support. However, the insulating support described in those patents is used for heating coil assembly that requires more components and costs more to build and assemble.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
To that end, the present invention provides a heating coil assembly having a metal bracket, a support rail, a heating coil, and a plurality of insulating supports. The metal bracket is attached to a terminal block and the support rail. The heating coil is electrically connected to the terminal block. Each insulating support has a hole to receive the support rail. Each insulating support further has a rigid body and a plurality of slots. Each slot is capable of receiving a portion of a coil turn of the heating coil. Each slot has a generally flat bottom and two inwardly projecting sidewalls. Each inwardly projecting sidewall is defined by a hook edge and ramp edge.
The rigid body of the insulating supports may further have generally parallel front and rear faces. The flat bottom of each slot prevents the coil turn from contacting the generally parallel front and rear faces. The hook edge of the inwardly projecting sidewall is capable of engaging the inner surface of the coil turn. The ramp edge of the inwardly projecting sidewall assists in sliding the coil into the slot.
In another embodiment, the present invention provides an insulating support for a helical wire heating coil. The support includes a rigid body of insulating material and a plurality of first and second slots. The rigid body has an opening to receive a single support rail. The body further includes a first edge, a second edge, and generally parallel front and rear faces. The plurality of first slots are located on the first edge. The plurality of second slots are located on the second edge. Each of the first and second slots are capable of receiving a portion of a coil turn of the heating coil. Each of the first and second slots further include a generally flat bottom and two inwardly projecting sidewalls. The flat bottom of the slot prevents the coil turn from contacting the generally parallel front and rear faces of the body. Each inwardly projecting sidewall is defined by a hook edge and a ramp edge.
In further embodiment, the present invention includes a method of assembling a heating coil assembly. The method includes providing a support rail, a terminal block, a plurality of insulating supports, and a heating coil. The support rail has a longitudinal body and a bracket portion. The longitudinal body has a plurality of tabs. The terminal block has a bracket portion. The plurality of insulating supports have at least one slot and a hole. The method further includes: attaching the bracket portion of the support rail to the bracket portion of the terminal block; inserting the longitudinal body of the support rail in each hold of the insulating support; bending the plurality of tabs on the longitudinal body of the support rail to prevent axial movement of the insulating supports along the support rail; placing a turn of the heating coil in each slot of the insulating supports; and electrically connecting the heating coil to the terminal block.
The above summary of the present invention is not intended to represent each embodiment, or every aspect of the present invention. This is the purpose of the figures and detailed description which follow: